This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-222511, filed Aug. 5, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to an optical pickup device for recording/reproducing information in/from an optical storage medium, and more specifically, to an optical pickup device for recording/reproducing information in/from an optical storage medium capable of three-dimensional recording by a plurality of beams. Further, the invention relates to an optical information recording/reproducing apparatus using the optical pickup device.
Conventionally known is a technique for recording in or reproducing independent pieces of information from different depths in a recording layer of an optical storage medium.
An optical storage medium or optical disk in/from which information is recorded/reproduced has a relatively thick recording layer and a reflective layer for servo control. Information can be recorded in different depths in the recording layer.
An example of an optical pickup device for three-dimensional recording/reproducing operation is described in Jpn. Pat. Appln. KOKAI Publication No. 7-21565.
The optical pickup device is designed so that a servo beam is converged on a reflective layer of an optical disk, focus control and tracking control are carried out on the basis of light reflected by the reflective layer as a recording/reproducing beam is converged in a recording layer of the optical disk, and the physical properties of the recording layer are locally changed to effect information recording or information is reproduced on the basis of the reflected light.
In the optical pickup device, a collimator for a recording/reproducing light source is moved along its optical axis by an actuator, whereby the point of convergence of the recording/reproducing beam is moved along its optical axis for a distance corresponding to the movement of the collimator with respect to the point of convergence of the servo beam. Thus, the depth of the point of convergence of the recording/reproducing beam in the recording layer is controlled, that is, the recording surface is changed.
In the optical pickup device described above, the collimator for the recording/reproducing light source is moved to change the point of convergence of the recording/reproducing beam. Therefore, the parallelism of the recording/reproducing beam fluctuates as the collimator moves. The change of the parallelism of the recording/reproducing beam causes the incident beam diameter to change with respect to the effective diameter of an objective lens. This results in change of the coupling efficiency or optical transfer efficiency for the objective lens.
Thus, the movement of the collimator for changing the depth of the recording layer or changing the recording surface causes the coupling efficiency for the objective lens to change, so that optical power that reaches the recording layer is changed. This hinders reliable recording/reproducing operation.
In a so-called separated optical system, which includes a stationary optical system portion and a movable optical system portion that is only moved for access operation, in particular, fluctuation of the parallelism of the recording/reproducing beam inevitably causes the coupling efficiency for the objective lens to change in response to the movement of the movable optical system portion also.
Thus, the optical pickup device cannot steadily carry out high-density recording for mass storage, and is not applicable to the separated optical system for high-speed access.
The present invention has been contrived in consideration of these circumstances, and its object is to provide an optical pickup device capable of carrying out reliable recording/reproducing operation without any fluctuation of the parallelism of a recording/reproducing beam.